1. Field of the Invention
The present invention relates to a photoresist solution contained in a phosphor slurry which is applied to a color cathode ray tube(color CRT), and more particularly, to a photoresist solution composed of photosensitizer without heavy metal such as chromium , and an appropriate polymer, so as to improve an adhesive performance and remove a color residue of the color CRT made therewith.
2. Description of the Prior Art
Generally, a phosphor screen of the color CRT displays an image by exciting phosphor material deposition thereon. The phosphor screen is consisting of green, blue and red phosphor patterns and a black matrix disposed between the patterns.
The process for forming a black matrix comprises the steps of coating the photoresist on the inner surface of a panel, i.e., a front glass of the color CRT, coating graphite emulsion thereon, exposing it to light and developing to form a black matrix with graphite lines.
The process for forming green, blue and red phosphor patterns is called as a slurry process. The slurry process comprises the steps of cleaning the inner surface of the panel on which the black matrix was formed, and coating slurry, which is a mixture of the photoresist solution and a phosphor, on the inner surface of the panel. The slurry is prepared by mixing sodium dichromate in polyvinyl alcohol aqueous solution and suspending the phosphor therein.
A small quantity of surfactant is added to the slurry in order to improve the affinity for the front glass and the coating characteristics. After coating the slurry on the inner surface of the panel, the panel is rotated With 150 to 250 rpm to uniformly spread the slurry, and it is dried by the blower with an infrared heater. During the drying process, a covalent bond is formed on the inner surface of the front glass by an esterification reaction, and then the exposure step is proceeded.
The exposure step is to expose the black matrix and the photoresist solution of the slurry to an ultra violet light, so as to cure the polyvinyl alcohol and the sodium dichromate. By exposing the polyvinyl alcohol and the sodium dichromate to the ultraviolet light, they become insoluble to the water.
After the exposure step, the developing step is performed by washing off the uncured slurry from the panel with warm water, whereby the phosphor patterns are formed, in which phosphor cured by ultraviolet light is remained. The phosphor patterns are dried to be solidified by heater drying.
In prior art, polyvinyl alcohol polymer, and sodium dichromate as photosensitizer have been used in the step for forming the phosphor patterns. The chemical structure of polyvinyl alcohol polymer is as follows:
Formula 1 ##STR1##
However, the adhesive strength cf the red phosphor is relatively lower than those of the green and the blue phosphor. Thus, it is difficult to form uniform layer of phosphor screen and the color residue occurs in the color CRT made therewith. Further, the photoresist solution which contains the forbidden heavy metal, such as, chromium causes the environmental problems.
Also in the prior art, as an initiator for polymerizing, V-50 [(Wako chemical, 2,2'-Azobis (2-amino propane) dihydrochloride] is used.
However, there are problems that a Diazo photosensitizer is decomposed by hydrochloric acid contained in the initiator with the passage of time, and the stability is thus degraded in storage.